Normal pressure hydrocephalus (NPH) is a clinical syndrome characterized by enlargement of the brain's ventricular spaces without obstruction of cerebrospinal fluid (CSF) or elevation in CSF pressure. This condition may develop from a variety of processes that cause decreased resorption or over-production of CSF. The net effect of NPH is a reduction in the compliance of the brain parenchyma resulting in an increased susceptibility to brain injury. NPH is often associated with disturbances in gait, urinary continence and cognitive abilities.
It is known that the diffusion of water in the periventricular region is altered in hydrocephalic patients due to transependymal resorption of CSF. This fluid diffuses away from the ventricular surface producing increased extracellular water in the periventricular white matter (PVWM). Thus it is known that the average diffusion constant of the PVWM in hydrocephalic patients is increased compared to normals. Using magnetic resonance imaging (MR) and utilizing skill and judgment of the diagnostician in isolating an appropriate region of interest (ROI), it is possible to observe the evidence of this increased average diffusion content of the PVWM. However, as a useful tool in diagnosis, this procedure has its limitations.